The present invention generally relates to cleaning and polishing devices for use in critical environments, and in particular, to a cleaning/polishing pad which has a selected surface pattern for use as a circular or roller brush and as a manual wipe, and a method for using the pad.
Many industrial operations, especially in semiconductor manufacturing operations, require efficient means to polish and clean highly finished surfaces. Semiconductor materials, such as silicon wafers, require the removal of particulates and other surface contaminants during the manufacturing processes. Other materials, such as optical glass or magnetic storage devices, also require similar removal of particulates and other surface contaminants. In particular, operations in semiconductor device fabrication often utilize a two-step process that includes a polishing step followed by a brushing step. One of the main goals of the polishing step is to planarize the wafer, while the main goal of the brushing step is to perform subsequent cleaning of the wafer. These two-steps are often repeated followed by the addition of semiconductor material in order to manufacture a semiconductor material having multiple polished layers. It is essential that particulates and surface contaminates be removed between the layers to avoid defects in the final product.
In the manufacturing of integrated circuits, chemical mechanical polishing has emerged as the preferred approach to achieve both local and global planarization. These techniques typically use a polishing pad along with a polishing slurry. The brushing step, which follows chemical mechanical polishing, typically involves cleaning fluid and a brush device having a sponge-type cleaning pad.
Popular brushes, rollers, sponges and other wiping products made from non-woven, woven or knit materials, typically used in industrial and critical environments, are inadequate to address the higher levels of cleanliness and absorbency required in cleaner environments. Unfortunately, fiber particulates and certain free polymers found on conventional wiping products, frequently contaminate the processes, tools and facilities. In addition to the surface of the manufactured item, the environment and work surfaces in microelectronic firms are susceptible to such contamination. Prior art wipes, sponges or brushes, which have conventional nubs, damage surface features and are very poor at delivering cleaning chemicals to the surface of wafers and other media. Other prior art wipes, sponges or brushes contain chloride and other biocides which are corrosive to disk media surfaces. Also, undesirable metallization of semiconductor wafers might occur when metal particulates are produced by conventional wiping products. Furthermore, silicone has also been used when cleaning, but is not permitted with semiconductor wafers as it is detrimental to the surface of the wafers. Therefore, silicone is not permitted in any product used in the cleaning process.
One method for cleaning wafers involves pads that contact and clean the wafer as they rotate. U.S. Pat. No. 5,778,481 (""481), assigned to International Business Machines Corporation, describes disc shaped cleaning/polishing pads having resilient members (nubs) arranged in patterns (spiral, swirl, concentric or the like) which facilitate the movement of cleaning/polishing fluids from the center of the pads to the periphery. The pads of the ""481 patent may be composed of suitable materials such as polyurethane or polyvinyl alcohol.
Likewise, U.S. Pat. No. 5,311,634, issued to Nicholas Andros, describes disc shaped cleaning pads for use on a cleaning apparatus, which consist of a supporting core with a sponge affixed thereto which is a microporous hydroxylated polymer material; the surface of the sponge is convex having a plurality of projections which are preferably a plurality of hemispherical nubs arranged in concentric circles, which may also be ellipsoid, cubic, conical or a variety of other shapes, radiating from the central axis of the sponge.
Furthermore, U.S. Pat. No. 5,966,766, assigned to Advanced Micro Devices, Inc., shows a method and apparatus for cleaning a semiconductor wafer that includes a disc-shaped brush which is a substantially flexible material having a plurality of protrusions thereon; the protrusions are designed to extend through corresponding openings in a disc shaped base wherein the protrusions are spaced apart.
Alternative methods involve the use of sponge or sponge-like rollers for automated machinery, and wipes to manually clean surfaces. U.S. Pat. Nos. 6,004,640 and 5,460,655, assigned to Wilshire Technologies, Inc., disclose a hydrophilic foam article and surface-cleaning method for a clean room which article is made from an open cell, static-dissipative, polyurethane foam and laundered in deionized water, and can be fashioned as a wiper, a sponge, a roller, a swab mounted on a handle, or a plug having a generally cylindrical shape.
Also, U.S. Pat. No. 6,004,402 (""402), assigned to Xomed Surgical Products, Inc., shows a method of cleaning silicon material with a sponge in which the sponge is purified to remove undesirable residual contaminants. The sponge of the ""402 patent has 100% open pores and no dead ends or fibrils. Furthermore, the sponge therein also has conical projections extending from the outer surface. The projections are disposed at regular intervals in rows offset from one another in the direction of the longitudinal axis, and have planar surfaces, which are smaller than their bases.
U.S. Pat. No. 4,566,911 (""911), assigned to Kanebo Limited, describes a method for cleaning an article using a cleaning roll having a surface layer of polyvinyl acetal porous elastic material. The roller of the ""911 patent may have a smooth surface, a gear-like surface with parallel groves which may form an angle to a roll axis, or projections extending from the surface in which the projections may be circular, ellipsoidal, rectangular, or diamond shape or the like which covers a surface area of 15% to 65% of the entire surface area. The articles of the ""911 patent is not designed for use in a critical environment.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.
Cleaning pads of the present invention may be used in brushes which are used in chemical mechanical planarization washing, wet bench photoresist, etching techniques, spin drying, disk media washing, substrate washing, and other microelectronic/optical washing and drying processes. Alternatively, the cleaning pads may be used as manual abrasive and wiping pads which are used to apply or remove cleaning chemicals, debris, residues and particles, and to dry surfaces by hand. The cleaning pads facilitate the application of cleaning/polishing chemicals via external delivery, internal delivery, and submerged into the cleaning chemicals.
It is an object of the present invention to provide a cleaning pad surface which generates turbulence in the fluid cleaning chemicals as the pad is moved across a substrate. The cleaning pad of the present invention has at least one surface designed to contact the item to be cleaned. This surface has evenly distributed nubs with troughs interspersed between the nubs. When properly used, the nubs agitate the fluid cleaning chemicals creating sufficient agitation to remove particulates from the item.
A further object of the present invention is to provide a cleaning pad which permits fluid to be dispersed through the pad or to wick into the pad. The present pad has a micropore structure which is open-celled having very fine pores on the order of 2-5 microns. These pores permit the cleaning fluid to be dispersed and removed through the pad. This attribute permits control of the amount of cleaning chemicals present.
Another object of the present invention is to increase the absorbency of cleaning pads or wipes for clean environments. The absorbency of a cleaning pad according to the present invention may be selectively controlled with automated systems. Otherwise, the cleaning pads according to the present invention are highly absorbent.
Yet another object is to control the delivery of cleaning chemicals. The open-cell core of the pad permits even flow of cleaning chemicals, which flow can be modulated by applying a vacuum or pressure across the opposing side of the pad. The present invention facilitates delivery of cleaning chemicals continuously on and into the face of the wafer with higher rates of turbulence and greater flushing and drawing of debris, residues and particles than prior art articles.
A further object of the present invention is to improve the longevity of cleaning pads as long-term disposables. The pads of the current invention have a longer life than prior art cleaning wipes/sponges but are still disposable. The prior art devices have sharp or squared edges which catch on rough substrates resulting in torn wipes or sponges. The pads of the present invention have no sharp or squared edges, and therefore do not tear easily.
Another object of the present invention is to eliminate fiber release from fiber based wiping materials. The uniformity of cells prevents dry spots which might otherwise result in subsequent abrasion that shortens the life of the brush. Also, uniformity limits the transmission of brush particles to the wafer.
It is also an object of the present invention to reduce damage to the item cleaned. Sharp edges are avoided in the present invention, as previously mentioned, which reduces scratching of the item cleaned. Prior art articles have sharp edges which are especially undesirable in the manufacture of semiconductor materials, especially silicon wafers. The nubs on the cleaning pads of the present invention have rounded edges and corners thus eliminating this potential source of scratches.
These and other objects of the present invention will become readily apparent upon further review of the following drawings and specification.